EP1311006A1 - Thin-film piezoelectric element - Google Patents
Thin-film piezoelectric element Download PDFInfo
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- EP1311006A1 EP1311006A1 EP01953307A EP01953307A EP1311006A1 EP 1311006 A1 EP1311006 A1 EP 1311006A1 EP 01953307 A EP01953307 A EP 01953307A EP 01953307 A EP01953307 A EP 01953307A EP 1311006 A1 EP1311006 A1 EP 1311006A1
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- thin film
- piezoelectric
- piezoelectric thin
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/80—Constructional details
- H10N30/85—Piezoelectric or electrostrictive active materials
- H10N30/853—Ceramic compositions
- H10N30/8548—Lead-based oxides
- H10N30/8554—Lead-zirconium titanate [PZT] based
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/20—Piezoelectric or electrostrictive devices with electrical input and mechanical output, e.g. functioning as actuators or vibrators
- H10N30/204—Piezoelectric or electrostrictive devices with electrical input and mechanical output, e.g. functioning as actuators or vibrators using bending displacement, e.g. unimorph, bimorph or multimorph cantilever or membrane benders
- H10N30/2047—Membrane type
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/01—Manufacture or treatment
- H10N30/07—Forming of piezoelectric or electrostrictive parts or bodies on an electrical element or another base
- H10N30/074—Forming of piezoelectric or electrostrictive parts or bodies on an electrical element or another base by depositing piezoelectric or electrostrictive layers, e.g. aerosol or screen printing
- H10N30/076—Forming of piezoelectric or electrostrictive parts or bodies on an electrical element or another base by depositing piezoelectric or electrostrictive layers, e.g. aerosol or screen printing by vapour phase deposition
Definitions
- the present invention relates to a piezoelectric element using a piezoelectric thin film material.
- a piezoelectric substance is made into different piezoelectric elements according to different kinds of objects, and the elements are widely used as functional electronic components, particularly including an actuator producing deformation by the application of a voltage and a sensor generating a voltage based on the deformation of its element in reverse.
- Pb-based dielectrics having a large piezoelectric characteristic, particularly perovskite type ferroelectrics of the Pb(Zr 1-x Ti x )O 3 family referred to as PZT, have been widely used until now, and they are usually formed by sintering oxides composed of individual elements.
- the forming of a piezoelectric element having a bimorph or unimorph structure is considered to be one of its applications.
- the value of a piezoelectric constant d31 is important as the piezoelectric characteristic.
- the piezoelectric thin film requires the value of the piezoelectric constant d31 equal to or more than - 100 pC/V, which is the same value as that of bulk materials.
- a substrate compatible with a process for making the other elements is required to be used for the piezoelectric thin film.
- a piezoelectric substance into a thin film for example, in case of forming piezoelectric substances collectively called PZT into a thin film, treatment at high temperatures or alternatively thin film growth on a substrate at a high temperature equal to or higher than 500°C needs to be performed, and thus large internal stress is to be left in the formed piezoelectric thin film during the process of cooling after the film formation.
- the residual stress causes the crystal structure of the film to be greatly different from a bulk material in quality, and often causes degradation in its piezoelectric characteristic and variations in its characteristic. From such reasons, the piezoelectric thin film is difficult to design as an actuator and a sensor, and thus there is not an example that a piezoelectric thin film has been put to practical use.
- the piezoelectric thin film As a micro-actuator or a micro-sensor, it is required to realize a high piezoelectric characteristic and also to decrease variations in the characteristic.
- the characteristic of the piezoelectric thin film greatly depends on the compositional structure of thin film materials and the crystal structure thereof. Further, the crystal structure of the piezoelectric thin film greatly depends on a substrate for forming it and a film-forming process.
- the piezoelectric thin film is applied as a piezoelectric element, it is required to obtain a high piezoelectric characteristic with stability even under an environment peculiar to the thin film, such as the above internal stress, and thus a process of making thin film and the development of a martial suitable for the thin film are demanded.
- the present invention is for solving the above problems and has an object to realize a piezoelectric thin film having a high piezoelectric characteristic even in the thin film, by controlling and optimizing the microscopic crystal structure of a piezoelectric thin film material, and to provide a thin film piezoelectric element which is able to withstand practical use. Also, the present invention has an object to realize a technology for forming, with stability, a piezoelectric thin film having the same high piezoelectric characteristic as that of a bulk material, by optimizing the material composition of the piezoelectric thin film and using a forming method in which composition is modulated, and to provide a thin film piezoelectric element which is practically usable as a micro-actuator or a micro-sensor.
- the thin film piezoelectric element according to the present invention preferably uses such a piezoelectric thin film that is a dielectric with the perovskite structure having lead, zirconium, and titanium as the main ingredients, and is in a composition region in which the Zr/ (Zr + Ti) ratio is equal to or more than 0.53 in the composition of the whole piezoelectric thin film, and has a crystal structure of the tetragonal system in which the c axis is longer than the a axis.
- this piezoelectric thin film is a dielectric with the perovskite structure having lead, zirconium, and titanium as the main ingredients, and is configured by a piezoelectric thin film in which the Zr/ (Zr + Ti) composition ratio of the surface portion is not less than 10% less than that of the substrate interface portion, and further the piezoelectric thin film is in a composition region in which the Zr/(Zr + Ti) ratio of the surface portion of this piezoelectric film is equal to 0.53 or more, and has a crystal structure of the tetragonal system in which the c axis is longer than the a axis is used.
- the substrate for forming the piezoelectric thin film has at least one of silicon, iron, magnesium oxide, alumina, and zirconia as the main ingredient, and the crystal structure of the piezoelectric thin film formed shows preferential orientation in the c axis, and the ratio c/a of the c axis to the a axis is within a range of not less than 1.01 and not more than 1.03, then the thin film piezoelectric thin film element having an excellent piezoelectric characteristic can be realized.
- FIG. 1 shows one embodiment of a thin film piezoelectric element according to the invention.
- a piezoelectric thin film 1 has a composition of Pb(Zr 1 - x Ti x )O 3 (0.47 x 1) (hereinafter, referred to as PZT) and has a film thickness of 3 ⁇ m.
- PZT Pb(Zr 1 - x Ti x )O 3 (0.47 x 1)
- This film was formed on a substrate 6 of magnesium oxide. Then, the substrate 6 was worked into a diaphragm structure and thus configured such that the piezoelectric thin film 1 can easily vibrate.
- the piezoelectric thin film 1 was formed by a sputtering method in which a sintered-body target having about the same composition as that of the formed thin film is placed in a vacuum chamber and plasma is generated over the target in a gas of an oxidizing atmosphere, thereby depositing the thin film 1 on the substrate 6 heated.
- the used substrate 6 of magnesium oxide is a single crystal substrate of the (100) plane, and a large number of grooves having a length of 500 ⁇ m and a width of 50 ⁇ m were formed in the substrate.
- One surface of the substrate 6 has a diaphragm structure where the surface is covered by a Pt lower electrode layer 3 of which is oriented to the (100) plane and has a thickness of 2 ⁇ m.
- the lower electrode layer 3 was made thicker than its usual thickness such that the layer 3 may act as a diaphragm for generating up-and-down vibrations from the expansion and contraction of the piezoelectric thin film 1.
- a single crystal substrate of magnesium oxide was used as the substrate, whereby the Pt lower electrode 3 was able to be easily oriented and also it was possible to control the orientation of the PZT piezoelectric thin film 1 to be formed thereon.
- a Pt upper electrode 4 having a thickness of 0.2 ⁇ m of the same shape as the diaphragm was formed at the positions corresponding to each diaphragm on the top of the piezoelectric thin film 1.
- this element By applying a voltage between the upper and lower electrodes, this element performs actuator operations.
- a sine wave of 1 kHz was applied between the upper and lower electrodes, and the evaluation of piezoelectric characteristics was performed by measuring up-and-down vibrations of the piezoelectric thin film 1 on the diaphragm.
- the amount of vibration was specified by a value measured at the center of the diaphragm where the amount of vibration becomes maximum.
- PZT materials change in the crystal structure according to the composition ratio of Zr to Ti, and in the composition ratio in which Zr/Ti is approximately 53/47, there exists a phase boundary between the tetragonal system and the rhombohedral system. It is known that a large piezoelectric characteristic is observed in the compositions near this phase boundary, because the phase structure becomes unstable therein.
- the internal stress of thin film materials can be controlled by adjusting various sputtering conditions.
- Zr/Ti of the phase boundary has rhombohedral structure in a composition ratio richer in zirconium than the ratio of 53/47, in which lattice deformation c/a becomes 1.
- the present invention by optimizing the process parameters such as a sputtering gas pressure, it was possible to control the stress in the piezoelectric thin film 1 composed of a PZT material and to change its crystal structure.
- the PZT thin film formed according to the present invention was subjected to crystal structure analysis using four-axis X ray diffraction, and concerning a PZT piezoelectric thin film of which Zr ratio is more than the Zr/Ti composition ratio of 53/47, it was found that the thin film also has a tetragonal crystal structure in which the c axis is longer than the a axis (Table 2).
- the values of its lattice deformation c/a was found to be in the range of 1.005 to 1.045.
- vibration characteristics of the thin film piezoelectric elements of FIG. 1 are compared with each other based on the crystal structures of the piezoelectric films.
- the piezoelectric thin films 1 formed as the tetragonal crystal structure and the piezoelectric thin films 1 formed as the usual rhoombohedral crystal structure were used, and a sine wave of 1 kHz and 10 V was applied across the thin films, and thus the amounts of piezoelectric vibration as piezoelectric actuators were measured.
- the piezoelectric thin films were formed such that their crystal structures might have the same rhombohedral system as a bulk material and the tetragonal system different from the bulk material.
- Zr/Ti composition ratio Tetragonal Rhombohedral Maximum (nm) Minimum (nm) Maximum (nm) Minimum (nm) 53/47 95 83 95 83 55/45 97 86 87 69 60/40 97 87 83 63 65/35 92 83 85 62 70/30 95 82 80 59 75/25 89 82 78 55
- Table 1 shows the maximum values and the minimum values of the amount of piezoelectric vibrations when twenty different thin film piezoelectric elements were used. Based on comparisons between the maximum values and minimum values, variations in the characteristic were evaluated. From Table 1, in a composition where the Zr/Ti ratio of the piezoelectric thin film 1 is richer in zirconium than 53/47, it was demonstrated that the PZT piezoelectric thin film 1 having the tetragonal crystal structure rather than the rhombohedral structure shows a stable vibration characteristic and generates excellent piezoelectric vibrations.
- the Pt lower electrode 3 By using a single crystal substrate of magnesium oxide as a substrate for forming the PZT piezoelectric thin film 1, the Pt lower electrode 3 could be easily made into a single crystal, and further the crystal control of the PZT piezoelectric thin film 1 could be realized.
- the micro crystal structure of the piezoelectric thin film 1 significantly affects the composition of the PZT thin film located near the interface with the substrate.
- a smaller Zr/Ti ratio of the substrate interface portion results in a better piezoelectric thin film having less defects and has a great effect on improvement and reduction of variations in the piezoelectric characteristic.
- the composition ratio of Zr/ (Zr + Ti) on the surface side of piezoelectric thin film 1 is 10% or more than 10% larger than that on the substrate interface side, excellent piezoelectric vibrations can be formed with stability. This is considered resulting from that the piezoelectric thin film 1 becomes easy to grow in a state having an excellent micro crystal structure.
- the piezoelectric vibration reflects the characteristic of the piezoelectric constant d31 of the piezoelectric thin film 1. As shown in Table 2, particularly, in crystal lattice deformation c/a within the range of 1.010 to 1.020, it was possible to generate excellent piezoelectric vibrations.
- the thin film piezoelectric element according to the present invention by controlling stress applied during forming the piezoelectric thin film and providing a piezoelectric thin film having the perovskite structure, it was possible to provide apiezoelectric thin film having an improved and stable characteristic.
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Abstract
To provide a piezoelectric thin film having an improved and stable characteristic by controlling stress applied during forming a piezoelectric thin film and providing the piezoelectric thin film having a perovskite structure. A thin film piezoelectric element in which a lower electrode is formed on a substrate, a piezoelectric thin film containing lead is formed on the lower electrode, and an upper electrode is further placed on the piezoelectric thin film, characterized in that the piezoelectric thin film is a dielectric with the perovskite structure having lead, zirconium, and titanium as the main ingredients, and is in a composition region in which, in the composition of the whole piezoelectric thin film, the Zr/(Zr + Ti) ratio is not less than 0.53, and has a crystal structure of the tetragonal system in which a c axis is longer than an a axis. <IMAGE>
Description
The present invention relates to a piezoelectric
element using a piezoelectric thin film material.
Generally, a piezoelectric substance is made into
different piezoelectric elements according to different
kinds of objects, and the elements are widely used as
functional electronic components, particularly
including an actuator producing deformation by the
application of a voltage and a sensor generating a voltage
based on the deformation of its element in reverse. As
a piezoelectric substance used for the applications of
actuators and sensors, Pb-based dielectrics having a
large piezoelectric characteristic, particularly
perovskite type ferroelectrics of the Pb(Zr1-xTix)O3
family referred to as PZT, have been widely used until
now, and they are usually formed by sintering oxides
composed of individual elements.
At present, as the trend toward smaller size and higher
performance of various electronic components advances,
smaller size and higher performance also are being
strongly demanded of the piezoelectric elements.
However, in piezoelectric materials made by a
manufacturing method centering on the sintering method,
a conventional manufacturing method, as the thickness
thereof is made thin, particularly as the thickness
approaches a thickness of about 10 µm, it gets nearer
to the size of the crystal grains constituting the
materials, and thus the effect of the crystal grains
becomes unable to be neglected. For this reason, there
arises a problem that variations and deterioration in
the characteristics become remarkable, and therefore,
in order to avoid this problem, a method of forming a
piezoelectric substance in which a thin film technology
or the like are applied as the change of the sintering
method has been studied in recent years.
Up to now, as a method of forming a thin film having
piezoelectric i.e. a piezoelectric thin film, chemical
vapor deposition methods evaporating and vaporizing
materials constituting a piezoelectric substance for
depositing them on a substrate, generally a rf sputtering
method and a MOCVD method, have been studied. However,
in piezoelectric thin films formed by these techniques,
there are large variations in their characteristics
caused by the problems of grain boundary and crystalline
orientation, when compared with the piezoelectric
characteristics of sintering-formed piezoelectric
materials referred to as bulk materials. Further, due
to the effects of stress applied to the piezoelectric
thin films, etc., the piezoelectric thin films have not
yet reached a point where they can provide a piezoelectric
characteristic enough to be practically used for sensors
and actuators or the like.
Particularly, in order to realize a micro-actuator
and a micro-sensor using a piezoelectric thin film, the
forming of a piezoelectric element having a bimorph or
unimorph structure is considered to be one of its
applications. However, in this case, the value of a
piezoelectric constant d31 is important as the
piezoelectric characteristic. To be put to practical use
as a micro-element, the piezoelectric thin film requires
the value of the piezoelectric constant d31 equal to or
more than - 100 pC/V, which is the same value as that
of bulk materials. Also, in case of considering
mass-production characteristics, a substrate compatible
with a process for making the other elements is required
to be used for the piezoelectric thin film. Thus, the
development of materials for a piezoelectric thin film
and the development of a manufacturing technology
therefor combined with the realization of high
piezoelectric are required.
However, in forming a piezoelectric substance into
a thin film, for example, in case of forming piezoelectric
substances collectively called PZT into a thin film,
treatment at high temperatures or alternatively thin film
growth on a substrate at a high temperature equal to or
higher than 500°C needs to be performed, and thus large
internal stress is to be left in the formed piezoelectric
thin film during the process of cooling after the film
formation. The residual stress causes the crystal
structure of the film to be greatly different from a bulk
material in quality, and often causes degradation in its
piezoelectric characteristic and variations in its
characteristic. From such reasons, the piezoelectric
thin film is difficult to design as an actuator and a
sensor, and thus there is not an example that a
piezoelectric thin film has been put to practical use.
In case of using the piezoelectric thin film as a
micro-actuator or a micro-sensor, it is required to
realize a high piezoelectric characteristic and also to
decrease variations in the characteristic. Usually, the
characteristic of the piezoelectric thin film greatly
depends on the compositional structure of thin film
materials and the crystal structure thereof. Further,
the crystal structure of the piezoelectric thin film
greatly depends on a substrate for forming it and a
film-forming process. When the piezoelectric thin film
is applied as a piezoelectric element, it is required
to obtain a high piezoelectric characteristic with
stability even under an environment peculiar to the thin
film, such as the above internal stress, and thus a process
of making thin film and the development of a martial
suitable for the thin film are demanded.
The present invention is for solving the above
problems and has an object to realize a piezoelectric
thin film having a high piezoelectric characteristic even
in the thin film, by controlling and optimizing the
microscopic crystal structure of a piezoelectric thin
film material, and to provide a thin film piezoelectric
element which is able to withstand practical use. Also,
the present invention has an object to realize a technology
for forming, with stability, a piezoelectric thin film
having the same high piezoelectric characteristic as that
of a bulk material, by optimizing the material composition
of the piezoelectric thin film and using a forming method
in which composition is modulated, and to provide a thin
film piezoelectric element which is practically usable
as a micro-actuator or a micro-sensor.
In a thin film piezoelectric element in which a lower
electrode is formed on a substrate, a piezoelectric thin
film containing lead is formed on the lower electrode,
and an upper electrode is further placed on the
piezoelectric thin film, the thin film piezoelectric
element according to the present invention preferably
uses such a piezoelectric thin film that is a dielectric
with the perovskite structure having lead, zirconium,
and titanium as the main ingredients, and is in a
composition region in which the Zr/ (Zr + Ti) ratio is
equal to or more than 0.53 in the composition of the whole
piezoelectric thin film, and has a crystal structure of
the tetragonal system in which the c axis is longer than
the a axis.
Further, in a thin film piezoelectric element where
a lower electrode formed on a substrate, a piezoelectric
thin film containing lead is formed on the lower electrode,
and an upper electrode is further placed on the
piezoelectric thin film, it is more advantageous that
this piezoelectric thin film is a dielectric with the
perovskite structure having lead, zirconium, and titanium
as the main ingredients, and is configured by a
piezoelectric thin film in which the Zr/ (Zr + Ti)
composition ratio of the surface portion is not less than
10% less than that of the substrate interface portion,
and further the piezoelectric thin film is in a composition
region in which the Zr/(Zr + Ti) ratio of the surface
portion of this piezoelectric film is equal to 0.53 or
more, and has a crystal structure of the tetragonal system
in which the c axis is longer than the a axis is used.
Also, if the substrate for forming the piezoelectric
thin film has at least one of silicon, iron, magnesium
oxide, alumina, and zirconia as the main ingredient, and
the crystal structure of the piezoelectric thin film
formed shows preferential orientation in the c axis, and
the ratio c/a of the c axis to the a axis is within a
range of not less than 1.01 and not more than 1.03, then
the thin film piezoelectric thin film element having an
excellent piezoelectric characteristic can be realized.
A configuration of a piezoelectric element according
to one embodiment of the invention will be described with
reference to a drawing.
FIG. 1 shows one embodiment of a thin film
piezoelectric element according to the invention. A
piezoelectric thin film 1 has a composition of Pb(Zr1 -
xTix)O3 (0.47 x 1) (hereinafter, referred to as PZT)
and has a film thickness of 3 µm. This film was formed
on a substrate 6 of magnesium oxide. Then, the substrate
6 was worked into a diaphragm structure and thus configured
such that the piezoelectric thin film 1 can easily vibrate.
Herein, the piezoelectric thin film 1 was formed by
a sputtering method in which a sintered-body target having
about the same composition as that of the formed thin
film is placed in a vacuum chamber and plasma is generated
over the target in a gas of an oxidizing atmosphere, thereby
depositing the thin film 1 on the substrate 6 heated.
The used substrate 6 of magnesium oxide is a single
crystal substrate of the (100) plane, and a large number
of grooves having a length of 500 µm and a width of 50
µm were formed in the substrate. One surface of the
substrate 6 has a diaphragm structure where the surface
is covered by a Pt lower electrode layer 3 of which is
oriented to the (100) plane and has a thickness of 2 µm.
The lower electrode layer 3 was made thicker than
its usual thickness such that the layer 3 may act as a
diaphragm for generating up-and-down vibrations from the
expansion and contraction of the piezoelectric thin film
1. A single crystal substrate of magnesium oxide was used
as the substrate, whereby the Pt lower electrode 3 was
able to be easily oriented and also it was possible to
control the orientation of the PZT piezoelectric thin
film 1 to be formed thereon.
A Pt upper electrode 4 having a thickness of 0.2 µm
of the same shape as the diaphragm was formed at the
positions corresponding to each diaphragm on the top of
the piezoelectric thin film 1. By applying a voltage
between the upper and lower electrodes, this element
performs actuator operations. At this time, a sine wave
of 1 kHz was applied between the upper and lower electrodes,
and the evaluation of piezoelectric characteristics was
performed by measuring up-and-down vibrations of the
piezoelectric thin film 1 on the diaphragm. The amount
of vibration was specified by a value measured at the
center of the diaphragm where the amount of vibration
becomes maximum.
Usually, PZT materials change in the crystal
structure according to the composition ratio of Zr to
Ti, and in the composition ratio in which Zr/Ti is
approximately 53/47, there exists a phase boundary
between the tetragonal system and the rhombohedral system.
It is known that a large piezoelectric characteristic
is observed in the compositions near this phase boundary,
because the phase structure becomes unstable therein.
On the other hand, in the case of thin film materials,
the processes of the sputtering method and CVD method
cannot provide as excellent composition controllability
as the sintering process does . Further, due to the effect
of the stress incurred from the substrate 6, the actual
crystal structure is often different from that of a
sintered body, thus resulting in a great change in the
piezoelectric characteristic of the piezoelectric thin
film 1. For this reason, a piezoelectric thin film
material having an excellent piezoelectric
characteristic and providing excellent reproducibility
has not been put to practical use.
In the case of the sputtering method, the internal
stress of thin film materials can be controlled by
adjusting various sputtering conditions. Usually, in
the bulk materials, Zr/Ti of the phase boundary has
rhombohedral structure in a composition ratio richer in
zirconium than the ratio of 53/47, in which lattice
deformation c/a becomes 1.
According to the present invention, by optimizing
the process parameters such as a sputtering gas pressure,
it was possible to control the stress in the piezoelectric
thin film 1 composed of a PZT material and to change its
crystal structure.
That is, the PZT thin film formed according to the
present invention was subjected to crystal structure
analysis using four-axis X ray diffraction, and
concerning a PZT piezoelectric thin film of which Zr ratio
is more than the Zr/Ti composition ratio of 53/47, it
was found that the thin film also has a tetragonal crystal
structure in which the c axis is longer than the a axis
(Table 2). The values of its lattice deformation c/a was
found to be in the range of 1.005 to 1.045.
In Table 1, vibration characteristics of the thin
film piezoelectric elements of FIG. 1 are compared with
each other based on the crystal structures of the
piezoelectric films. In the composition region in which
Zr/Ti is from 53/47 to 80/20, the piezoelectric thin films
1 formed as the tetragonal crystal structure and the
piezoelectric thin films 1 formed as the usual
rhoombohedral crystal structure were used, and a sine
wave of 1 kHz and 10 V was applied across the thin films,
and thus the amounts of piezoelectric vibration as
piezoelectric actuators were measured. Further, by
controlling the internal stress of the PZT piezoelectric
thin film of each composition, the piezoelectric thin
films were formed such that their crystal structures might
have the same rhombohedral system as a bulk material and
the tetragonal system different from the bulk material.
| Zr/Ti composition ratio | Tetragonal | Rhombohedral | ||
| Maximum (nm) | Minimum (nm) | Maximum (nm) | Minimum (nm) | |
| 53/47 | 95 | 83 | 95 | 83 |
| 55/45 | 97 | 86 | 87 | 69 |
| 60/40 | 97 | 87 | 83 | 63 |
| 65/35 | 92 | 83 | 85 | 62 |
| 70/30 | 95 | 82 | 80 | 59 |
| 75/25 | 89 | 82 | 78 | 55 |
Table 1 shows the maximum values and the minimum values
of the amount of piezoelectric vibrations when twenty
different thin film piezoelectric elements were used.
Based on comparisons between the maximum values and
minimum values, variations in the characteristic were
evaluated. From Table 1, in a composition where the Zr/Ti
ratio of the piezoelectric thin film 1 is richer in
zirconium than 53/47, it was demonstrated that the PZT
piezoelectric thin film 1 having the tetragonal crystal
structure rather than the rhombohedral structure shows
a stable vibration characteristic and generates excellent
piezoelectric vibrations.
By using a single crystal substrate of magnesium oxide
as a substrate for forming the PZT piezoelectric thin
film 1, the Pt lower electrode 3 could be easily made
into a single crystal, and further the crystal control
of the PZT piezoelectric thin film 1 could be realized.
Also, in the cases where silicon, iron, alumina, or
zirconia was used as the substrate, by optimizing
conditions for forming the Pt lower electrode 3, it was
possible to form the Pt lower electrode layer 3 in which
(100) Pt existed, and also it was possible to form the
piezoelectric thin film 1 having the same characteristic
as the magnesium-oxide substrate.
In case of using PZT as the piezoelectric thin film
1, it is known that the composition ratio of Zr to Ti
as well as the crystalline of the piezoelectric thin film
1 greatly affects the piezoelectric characteristic.
Therefore, the correlation between film structures
including crystalline and composition and piezoelectric
characteristics was studied.
As a result of the study, it became apparent that
the micro crystal structure of the piezoelectric thin
film 1 significantly affects the composition of the PZT
thin film located near the interface with the substrate.
Particularly, it was recognized that a smaller Zr/Ti ratio
of the substrate interface portion results in a better
piezoelectric thin film having less defects and has a
great effect on improvement and reduction of variations
in the piezoelectric characteristic.
Also, it was shown that, if particularly the
composition ratio of Zr/ (Zr + Ti) on the surface side
of piezoelectric thin film 1 is 10% or more than 10% larger
than that on the substrate interface side, excellent
piezoelectric vibrations can be formed with stability.
This is considered resulting from that the piezoelectric
thin film 1 becomes easy to grow in a state having an
excellent micro crystal structure.
On the other hand, in a tetragonal PZT piezoelectric
thin film made with a Zr/Ti composition of 60/40, the
most suitable lattice deformation c /a for the
piezoelectric thin film was examined by measuring the
crystal lattice lengths in the c axis and a axis by means
of a four-axis X ray diffraction apparatus . Table 2 shows
the amount of piezoelectric vibration of the thin film
piezoelectric element (FIG. 1) using a PZT piezoelectric
thin film having the tetragonal crystal structure. With
the amount of vibration, it was examined how the ratio
of c /a changes according to the amount of vibration with
respect to the crystal deformation (c/a) of a PZT
piezoelectric thin film having the Zr/Ti ratio of 60/40.
| Lattice deformation c/a | Amount of vibration (nm) |
| 1.005 | 72 |
| 1.010 | 89 |
| 1.012 | 97 |
| 1.018 | 98 |
| 1.025 | 95 |
| 1.030 | 88 |
| 1.038 | 69 |
| 1.041 | 64 |
In Table 2, the piezoelectric vibration reflects the
characteristic of the piezoelectric constant d31 of the
piezoelectric thin film 1. As shown in Table 2,
particularly, in crystal lattice deformation c/a within
the range of 1.010 to 1.020, it was possible to generate
excellent piezoelectric vibrations.
From the above results, by forming a PZT piezoelectric
thin film as the tetragonal crystal structure which was
different from the substrate, variations in the vibration
characteristic could be decreased, and by keeping the
crystal deformation c/a in the range of 1.010 to 1.030,
it was possible to realize a practically useful
piezoelectric thin film element.
In the thin film piezoelectric element according to
the present invention, by controlling stress applied
during forming the piezoelectric thin film and providing
a piezoelectric thin film having the perovskite structure,
it was possible to provide apiezoelectric thin film having
an improved and stable characteristic.
Claims (3)
- A thin film piezoelectric element in which a lower electrode is formed on a substrate, a piezoelectric thin film containing lead is formed on said lower electrode, and an upper electrode is further placed on said piezoelectric thin film, characterized in that said piezoelectric thin film is a dielectric with a perovskite structure having lead, zirconium, and titanium as main ingredients, and is in a composition region in which the Zr/(Zr + Ti) ratio is equal to or more than 0.53 in the composition of the whole piezoelectric thin film, and has a crystal structure of a tetragonal system in which a c axis is longer than an a axis.
- A thin film piezoelectric element in which a lower electrode is formed on a substrate, a piezoelectric thin film containing lead is formed on said lower electrode, and an upper electrode is further placed on said piezoelectric thin film, characterized in that said piezoelectric thin film is a dielectric with a perovskite structure having lead, zirconium, and titanium as main ingredients, and is in a composition region in which, in the composition of the whole piezoelectric thin film, the Zr/ (Zr + Ti) composition ratio of the surface portion is not less than 10% less than the Zr/ (Zr+Ti) composition ratio of the substrate interface portion and the Zr/ (Zr + Ti) ratio of the surface portion is equal to 0.53 or more, and that said piezoelectric thin film has a crystal structure of a tetragonal system in which a c axis is longer than an a axis is used.
- The thin film piezoelectric element according to claim 1 or 2, characterized in that the substrate forming the piezoelectric thin film has at least one of silicon, iron, magnesium oxide, alumina, and zirconia as the main ingredient, and the crystal structure of the piezoelectric thin film formed is preferentially orientated in the c axis, and the ratio c/a of the c axis to the a axis is within a range of not less than 1.01 and not more than 1.03.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2000222271 | 2000-07-24 | ||
| JP2000222271 | 2000-07-24 | ||
| PCT/JP2001/006318 WO2002009204A1 (en) | 2000-07-24 | 2001-07-23 | Thin-film piezoelectric element |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| EP1311006A1 true EP1311006A1 (en) | 2003-05-14 |
| EP1311006A4 EP1311006A4 (en) | 2007-07-25 |
Family
ID=18716534
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP01953307A Withdrawn EP1311006A4 (en) | 2000-07-24 | 2001-07-23 | THIN FILM PIEZOELECTRIC ELEMENT |
Country Status (4)
| Country | Link |
|---|---|
| US (1) | US6900579B2 (en) |
| EP (1) | EP1311006A4 (en) |
| CN (1) | CN100347872C (en) |
| WO (1) | WO2002009204A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1953840A3 (en) * | 2007-01-31 | 2012-04-11 | Panasonic Corporation | Piezoelectric thin film device and piezoelectric thin film device manufacturing method and inkjet head and inkjet recording apparatus |
| GB2555835A (en) * | 2016-11-11 | 2018-05-16 | Univ Of The West Of Scotland | Ultrasound transducer |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7067414B1 (en) | 1999-09-01 | 2006-06-27 | Micron Technology, Inc. | Low k interlevel dielectric layer fabrication methods |
| WO2004001870A1 (en) * | 2002-06-24 | 2003-12-31 | Seiko Epson Corporation | Piezoelectric element and head for jetting liquid and method for manufacturing them |
| DE10348346A1 (en) * | 2002-10-17 | 2004-05-27 | Kyocera Corp. | Print head actuator for ink-jet printer, includes displacement element having piezoelectric ceramic layer and pair of electrodes |
| JP5063606B2 (en) | 2005-11-04 | 2012-10-31 | セラコンプ カンパニー， リミテッド | Piezoelectric single crystal and method for manufacturing the same, and piezoelectric applied parts and dielectric applied parts using the piezoelectric single crystal |
| JP5382905B2 (en) * | 2008-03-10 | 2014-01-08 | 富士フイルム株式会社 | Method for manufacturing piezoelectric element and method for manufacturing liquid discharge head |
| CN102569639B (en) * | 2012-01-06 | 2014-06-04 | 中国科学院宁波材料技术与工程研究所 | Preparation method for self-supporting piezoelectric/ferroelectric film |
| CN103378286B (en) * | 2012-04-19 | 2017-12-01 | 新科实业有限公司 | Thin film piezoelectric element and manufacturing method thereof, magnetic head folding sheet combination and disk driver |
| CN107342357B (en) * | 2016-04-28 | 2022-08-16 | 新科实业有限公司 | Thin film piezoelectric element and method for manufacturing the same |
| JP2019057570A (en) * | 2017-09-20 | 2019-04-11 | セイコーエプソン株式会社 | Piezoelectric element and liquid discharge head |
| CN109459068A (en) * | 2018-10-09 | 2019-03-12 | 佛山市卓膜科技有限公司 | A kind of precision piezoelectric sensor |
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|---|---|---|---|---|
| US6335622B1 (en) * | 1992-08-25 | 2002-01-01 | Superconductor Technologies, Inc. | Superconducting control elements for RF antennas |
| JPH06172027A (en) * | 1992-12-02 | 1994-06-21 | Toto Ltd | Ferroelectric porcelain composition |
| JPH08268756A (en) * | 1995-03-30 | 1996-10-15 | Toyota Central Res & Dev Lab Inc | Method for manufacturing ferroelectric ceramics |
| DE19712496A1 (en) * | 1996-03-26 | 1997-10-30 | Mitsubishi Materials Corp | Piezoelectric thin-film component |
| JPH10200369A (en) * | 1997-01-13 | 1998-07-31 | Mitsubishi Materials Corp | Piezoelectric thin film resonator |
| US5792379A (en) * | 1997-03-27 | 1998-08-11 | Motorola Inc. | Low-loss PZT ceramic composition cofirable with silver at a reduced sintering temperature and process for producing same |
| JP3666177B2 (en) * | 1997-04-14 | 2005-06-29 | 松下電器産業株式会社 | Inkjet recording device |
| US6123867A (en) * | 1997-12-03 | 2000-09-26 | Matsushita Electric Industrial Co., Ltd. | Piezoelectric ceramic composition and piezoelectric device using the same |
| JP4122564B2 (en) * | 1998-04-24 | 2008-07-23 | セイコーエプソン株式会社 | Piezoelectric element, ink jet recording head and manufacturing method thereof |
| JP4326151B2 (en) * | 1998-05-08 | 2009-09-02 | アバゴ・テクノロジーズ・ワイヤレス・アイピー（シンガポール）プライベート・リミテッド | Thin film piezoelectric vibrator |
| JP2003060252A (en) * | 2001-08-09 | 2003-02-28 | Matsushita Electric Ind Co Ltd | Piezoelectric actuator, ink jet head and ink jet recording apparatus |
| JP2003118104A (en) * | 2001-10-10 | 2003-04-23 | Matsushita Electric Ind Co Ltd | Sputtering target for forming ferroelectric film, ferroelectric film using the same, ferroelectric element and actuator using the same, inkjet head and inkjet recording apparatus |
-
2001
- 2001-07-23 US US10/333,705 patent/US6900579B2/en not_active Expired - Lifetime
- 2001-07-23 EP EP01953307A patent/EP1311006A4/en not_active Withdrawn
- 2001-07-23 WO PCT/JP2001/006318 patent/WO2002009204A1/en not_active Ceased
- 2001-07-23 CN CNB018133703A patent/CN100347872C/en not_active Expired - Lifetime
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1953840A3 (en) * | 2007-01-31 | 2012-04-11 | Panasonic Corporation | Piezoelectric thin film device and piezoelectric thin film device manufacturing method and inkjet head and inkjet recording apparatus |
| GB2555835A (en) * | 2016-11-11 | 2018-05-16 | Univ Of The West Of Scotland | Ultrasound transducer |
| GB2555835B (en) * | 2016-11-11 | 2018-11-28 | Novosound Ltd | Ultrasound transducer |
| EP3538289B1 (en) * | 2016-11-11 | 2022-06-01 | Novosound Ltd | Ultrasound transducer |
| US12453286B2 (en) | 2016-11-11 | 2025-10-21 | Novosound Ltd | Method for manufacturing an ultrasound transducer |
Also Published As
| Publication number | Publication date |
|---|---|
| WO2002009204A1 (en) | 2002-01-31 |
| US6900579B2 (en) | 2005-05-31 |
| EP1311006A4 (en) | 2007-07-25 |
| CN1444777A (en) | 2003-09-24 |
| CN100347872C (en) | 2007-11-07 |
| US20030173871A1 (en) | 2003-09-18 |
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